In a typical internal combustion engine cylinder block, the cooling jacket thereof is formed by interconnected side and end walls of the block coacting with a floor section. Cylinder tubes are formed within the block and extend, at least in part, upwardly into the jacket. A conventional piston assembly, including a piston head, piston rings, and a liner or core, is normally disposed within each cylinder tube. A cylinder head is compressed against the top surface of the block with a head gasket sandwiched therebetween, thereby forming a sealed coolant cavity around the cylinder tubes so that a liquid, such as water, may freely circulate with minimum obstruction and thus effectively remove excess heat from the tube walls via an external heat exchanger. Maintaining a freely flowing coolant around a substantial exterior portion of the cylinder tube is necessary and desirable for continuous and efficient engine operation. An individual combustion chamber is provided for each cylinder and is defined by the upper portion of the cylinder tube, or liner, the cylinder head and gasket overlying same, and the reciprocating piston head when the latter is at and near its top dead center position within the tube.
Normally, the cylinder tubes are free standing and independent of the surrounding block structure except for the floor section to which they are connected. Such a block is typically cast as a single piece. The free standing arrangement of the cylinder tubes maximizes cooling thereof, while at the same time a relatively high cylinder tube compliance results. With this arrangement, however, when the engine is assembled, the cylinder head is usually secured by a plurality of head bolts to the top of the block, causing a substantial axial compression to be exerted on the cylinder tubes engaged thereby. The head bolts are generally of uniform length and engage internally threaded openings, or bores, formed in the cooling jacket walls and in bosses disposed inwardly of such walls. The threads of each opening in the conventional block design normally commence at the same level relative to the top surface of the cylinder block. The jacket walls provide some axial support to those portions of the cylinder tubes proximate thereto, but as to the portions of cylinder tubes more distant from the jacket walls, there is little or no axial support by the latter. This nonuniform support results in relatively large axial and radial variations around the periphery of the tubes, thereby promoting substantial distortions thereof when the engine is assembled. These distortions shorten seal life, degrade seal efficiency, cause uneven combustion seal load distribution, promote uneven cylinder and piston ring wear, and in some instances may even cause engine failure resulting in a major overhaul.